Mechanical key actuator including a cantilever beam restoring force means

ABSTRACT

An actuating device having a keytop, base, and an actuator assembly affixed to the base, the assembly including a rod and a cantilever beam arrangement for providing a snap action response to key force and for driving the rod to form an electrical makebreak contact, the base and assembly constituting a unitary flexible-tough thermoplastic body.

United States Patent Kekas [451 June 6,1972

[54] MECHANICAL KEY ACTUATOR I INCLUDING A CANTILEVER BEAM RESTORINGFORCE MEANS [72] Inventor: Dennis H. Kekas, Raleigh, N.C.

[73] Assignee: International Business Machines Corporation, Armonk, NY.e

22 Filed: Jan. 4, 1971 21 Appl.No.: 103,557

3,582,584 6/1971 Best ..200/l68C Primary Exaniiner--H. 0. JonesAttorneyHanifin & Jancin and Robert B. Brodie [57] ABSTRACT An actuatingdevice having a keytop, base, and an actuator assembly affixed to thebase, the assembly including a rod and a cantilever beam arrangement forproviding a snap action response to key force and for driving the rod toform an electrical make-break contact, the base and assemblyconstituting aunitary flexible-tough thermoplastic body.

12 Claims, 6 Drawing Figures PATENTEBJIJN smz 3.666.356

FIG. 2a FlG.2b FlG.2c

INVENTOR DENNIS H. KEKAS ATTORNEY MECHANICAL KEY ACTUATOR INCLUDING ACANTILEVER BEAM RESTORING FORCE MEANS BACKGROUND OF THE INVENTIONDESCRIPTION OF THE PRIOR ART In the prior art, many examples ofmechanical actuating devices for use with electric switches may befound. Typically, the device comprises a keytop, a base or referencesurface, and an actuating assembly affixed to the base. The assemblyitself frequently comprises a rod engaging the keytop. The rod ismovable along a constrained path, responsive to manual pressure on thekey. At or towards the end of its travel, the rod drives an electricalmake-break contact. Repositioning of the rod after release of manualpressure or stroking is achieved by having the assembly include a springbias or other form of restoring force working opposite the force drivingthe rod.

. It has been found desirable to incorporate some form of tactilefeedback to the operator of the'key to indicate that the key stroke hasbeen completed. This is often accommodated by designing the restoringforce means to exhibit a linear force versus rod travel characteristicwhich at some point suddenly decays. Illustrative examples may be thesud den buckling of a restoring spring in compression or the snap of aflexible and stressed diaphragm being turned inside out.

An elastic diaphragm switch consists of a pair of conductive surfaces,spaced apart by an apertured insulator, electrical BRIEF DESCRIPTION OFTHE DRAWINGS FIG. la exhibits a partia lly exploded perspective view ofone embodiment of the actuating device including the keytop and theunitary body forming the base and actuator assembly.

FIGS. lb and 1c are respective perspective and bottom views of anotherembodiment of the actuating device.

contact being madeby bringing the two surfaces together through theaperture. At least one of the surfaces is moved to engage the othersurface by the action of an actuating device,

Keyboards are fabricated from distributing numbers of the actuatorsusually in matrix array opposite one of the dia hragm surfaces and overcorresponding apertures of the insulator. In order to minimizenon-uniform flexing of the relevant diaphragm surface, the force andtravel of the actuators must be uniform. Furthermore, it is desired tofoster a uniform tactile feedback and not one which varies with flexureas is the case with spring biased key stems. Lastly, the number ofseparate components adds to both cost anddecreaseof reliability.

SUMMARY OF THE INVENTION The foregoing disadvantages of the prior artare overcome by forming the base and actuating assembly including'therod and restoring force means as a unitary flexible-tough thermoplasticbody. The assembly includes a cantilever beam arrangement secured to thebase and connected to the rod by a rigid hinging engagement. As the rodtranslates, the movement is converted through the hinging engagementinto flexure of the beams. An acute angle between the beam and the axisof the hinging engagement to the rod is maintained. Rod is stopped asthe angle approaches 90. The composition of forces becomes substantiallynormal to the rod at this pointsuch that a sudden decay or decrease inthe restoring force is sensed. This constitutes the tactile feedback.

The rod is repositioned when manual pressure is removed. This is due tothe force component operating on the rod through the hinges becomingmore longitudinal as the beams return to their unflexed position, andthe angle becomes more acute.

- The cantilever beam arrangement may preferably be embodied as a pairof spaced longitudinal members or as a substantially cylindricallyshaped flexing member surrounding a portion of therod. In the firstembodiment, rigid members may be hinged to the rod and correspondinglongitudinal members by very thin hinging segments. Each hinging segmentis formed from thinned cross sections of the thermoplastic in which thelong chain polymers have an orientation transverse to the axis ofthehinge. Similarly, the same hinging segments can also be fashioned forthe flexible diaphragm securing the cylindrical shaped flexing member.

FIGS. 2a, b, and c respectively show the actuating device in itsunstroked restored position, its stroked distended position, and in anelevation cut-away view.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to FIG. In of thedrawings, there is shown a partially exploded perspective view of oneembodiment of the invention. Keytop l is illustrated as a separatemoldable part used as a finger strokable surface. It is fashionedsufficiently large to satisfy the dimensional requirements normallyimposed on manually operable keytops found for example on typewritersand adding machines.

Base 3 and actuating assembly 5 constitute a unitary body formed fromany thermoplastic material or material exhibiting athermoplastic-elastomeric response. The material should preferably beselected from at least one of the group consisting of polypropylene,nylon, delrin, polyphenylene oxide, and an injection moldablepolyurethane. One materialfound especially significant was polypropylene20 percent or less volume filled with antimony oxide. The materialsaspect of this invention will be described subsequently in greaterdetail.

The base 3 forms a rigid reference surface to which the actuationassembly is secured and the-movement of the keytop and assembly partsreferenced. In this regard, the base thickness dimension is selected toobtain the desired rigidity.

The actuator assembly 5 comprises an actuating rod 13 freelytranslatable through an aperture 9 in base 3. Longitudinal members 15and 17 form a cantilever arrangement with rod 13 through hinging members19 and 21. One end of the longitudinal members is moldably secured tothe base. The other end is moldably fastened to the hinging members. Inturn, the hinging members are moldably fastened to the rod. Lastly, rodend 23 mechanically engages protrusion 11 of keytop 1 to complete theactuating device.

Referring now to FIG. 2a, there is shown the actuating device ,in itsrest or non-finger stroked position. The keytop l is fixedly mounted onthe rod end so that its bottom edge 22 extends a distance d above thebase surface 25. Longitudinal members 15 and 17 fonn a cantilever beamarrangement secured to base 3 at one of their respective ends. Members19 and 21 of length l hinge the beams to rod 13. They thereby define anacute angle 0 between member 19 and beam 15 and a member 21 and beam 17.The requirement of acuteness of angle 6 may be restated as 0 should bein the range defined by actuating device is ordinarily used to distend,for example, an

elastic diaphragm switch 25, 27, 29. Such a switch has a pair ofdeformable conductive surfaces 25 and 29 spaced apart by an aperturedinsulating layer 27.

Keytop l, in FIG. 2b is manually depressed such that rod 13 translatesdownward through distance d. This translation is converted into anequivalent bending moment about beams 15 and 17 through correspondinghinge members .19 and 21. The deflective loading and beam shaping anddisplacement of the beams for any constitutive material may bedetermined by reference to any standard treatise in strength ofmaterials such as, Strength of Materials by Timoshenko, Vol. 1 and 2, AVan Nostrand Reinhold Co., 450 33rd St., N. Y. 10001, copyright 1955.The bending moment restores the rod 13 to the position shown in FIG. 2aupon the release of keytop 1.

In order to form a unitary body of the base and actuator assembly, thematerial selected and its preparation should receive carefulconsideration. It is evident referencing FIGS. 2a and b that thematerial must be rigid at base 3 and the base attached portions of beams15 and 17 and rod 13. Hinge members 19 and 21 must be sufficiently rigidto transmit the bending force to displace beam ends 15 and 17. Notably,the beams must be susceptible of flexure. Concomitantly, materialforming the actual hinging engagements 33 and 35 must also besubstantially elastomeric. In order to fabricate both a unitary body anda reliable hinge" it was found that a material forrnable by a moldingprocess would be advantageous.

It was unexpectedly discovered that flexible-tough thermoplastics couldbe molded, i.e., injection molded into a unitary body and thatflexible-tough therrnoplastics also had long oriented polymer chainswhich constituted a good hinge.

Some therrnoplastics such as plexiglas are rigid and brittle materials.Normally, such thermoplastics do not have the stretch or elasticrecovery for hinge flexing purposes. However, polypropylene, nylon,delrin, polyphenylene oxide, and moldable polyurethanes exhibited theappropriate mechanical and fabrication characteristics. Accordingly,thermoplastics having the flexure-elastic properties of interest aredenominated flexible-tough therrnoplastics. In contrast, thermosettingmaterials except for hard rubbers do not exhibit the desired rigidityand furthermore do not have orientable polymer chains for the desiredhinge action.

Referring now to FIG. 20, there is shown a cut-away or sectional view ofthe actuator in its undistended position. Keytop l is set forth as amolded piece separated from rod 13 and base 3. Protrusion 11 of thekeytop constitutes a stem having a keyway 37 into which key 23 of therod may be snugly fitted. The keytop also has a hollowed out cavity 45formed interior which generates a distinctive acoustic snap when thecavity is brought into sharp contact with base 3.

In FIG. 2c, the base, rod, and translating means such as rigid members19 and 21 and their hinging attachments 33 and 35 are formed from thesame material. In this regard, it was found that an injection moldingprocess could be used. The process comprised the steps of gatingmaterial into the mold positioned as in FIGS. 2a, b, and along the outerbase and flowing the material down the beam sections and 17, across theouter hinge 33 to inner hinge 35, and finally into rod 13. This mannerof flowing the material under suitable pressure and temperature servesto align the polymer chains in a plane transverse to the hinge axes.This polymer chain orientation will produce a hinge capable of sustainedflexing and reflexing. Note also, that lip 7 may be molded as part ofbase 3. Lip 7 is designed to engage apertured retaining plate 43. Anyrigid plate can be used and against whose apertured sides lip 7 isflexed.

Referring now to FIG. lb, there is shown another embodiment of theinvention. In this embodiment, a longitudinally slotted cylindricalshell 47 replaces beams 15 and 17 shown in FIG. la. One end of thecylindrical shell is moldably secured to base 3. The shell surrounds atleast a portion of the rod extent. The shell ls longitudinally slotted49 to permit flexure of the other end.

In FIG. 10, a bottom view of the assembly illustrated in FIG. lb is setforth. A rigid diaphragm 51 is hingedly attached 33 to the cylindricalend along the diaphragm outer periphery. It is likewise hingedlyattached 35 to rod 13 towards the nose end 31. Flexure is achieved inthe same manner as shown in FIGS. 2a, b, and c.

It is contemplated that the embodiments will be considered for use onlyin a suitable temperature environment. That is, recognition must beaccorded both the limits as well as the advantages of thermoplasticmaterials. Furthermore, some variation in material flexibility andtoughness may occur as a function of the tacticity of the thermoplastic.

It should be noted that flexure and hinge performance varies inverselywith hinge thickness. Relatedly, hinge thicknesses in the range between0.010 to 0.001 are adequate.

This description of the present invention has been given as an exampleand it will be understood that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In an actuating device more particularly adapted to electric switchesand having a keytop, a base, and an actuator assembly affixed to thebase, the assembly including an actuating rod mechanically engaging thekeytop, and means for translating the rod along a defined path relativeto the base responsive to keytop stroking, and for restoring the rod toits former position in the absence of stroking, the base and theassembly constituting a unitary flexible tough thermoplastic body;wherein the translating means comprise:

hinging means;

a first and second rigid member;

a first and second beam member secured to the base at one of their endsand forming at the other of their ends a hinging engagement with the rodthrough the hinging means and the corresponding rigid member, each beammember being deflected by a corresponding rigid member as the rodtranslates; and

means for limiting the excursion of the rod such that an acute angle ismaintained between the longitudinal axis of each beam member and theaxis of the hinging means and corresponding rigid member.

2. In an actuating device according to claim 1, wherein:

the flexible-tough thermoplastic body is formed from a material selectedfrom at least one of the group consisting of polypropylene, nylon,delrin, polyethylene, polyphenylene oxide, and injection moldablepolyurethane.

3. In an actuating device according to claim 1, wherein:

the keytop forms a substantially hollowed out cavity facing one surfaceof the base and being spaced apart therefrom such that a distinctacoustic wave is generated upon the keytop being stroked and the cavityimpacting the base surface.

4. In an actuating device more particularly adapted to electric switchesand having a keytop, a base, and an actuator assembly affixed to thebase; the assembly including an actuating rod mechanically engaging thekeytop; and means for translating the rod along a defined path relativeto the base responsive to keytop stroking, and for restoring the rodposition in the absence of stroking, the base and assembly constitutinga unitary flexible tough body; wherein:

the translating means comprise:

a cantilever beam arrangement secured to the base at one end thereof andfurther including means for forming a spaced and rigid hingingengagement between the other end of the beam arrangement and the rod,the beam arrangement flexing as the rod translates: and

means for limiting the excursion of the rod such that an acute angle ismaintained between the flexing beam arrangement and the axis of itsspaced and rigid hinging engagement to the rod.

5. In an actuating device according to claim 4, wherein:

the cantilever beam arrangement comprises:

a substantially cylindrically shaped flexing member surrounding at leasta portion of the rod extent, the cylindrical flexing member beingsecured to the base at one of its ends; and

rigid diaphragm means hingedly attached to the other cylindrical flexingmember end along the diaphragm outer periphery and hingedly attached tothe rod along the diaphragm inner periphery.

6. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed from aflexible-tough thermoplastic material.

7. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed from amaterial selected from at least one of a group of materials consistingof polypropylene, nylon, delrin, polyethylene, polyphenylene oxide, andmoldable polyurethanes.

8. In an actuating device according to claim 4, wherein:

the base and assembly constituting the unitary body are formed frompolypropylene suffused with antimony oxide.

9. In an actuating device according to claim 8, wherein:

the antimony oxide constitutes no more than 20 percent of the propyleneand antimony oxide volume.

10. In an actuating device according to claim 4, wherein:

each hinging engagement is fashioned from a segment of thermoplasticmaterial having a cross section thickness T parallel to the hinging axisin the range 0.001 inches T s 0.01 inches and further wherein the longchain polymers are oriented transverse to the hinging axis.

11. in a mechanical key actuator having a keytop, a base, and anactuator assembly affixed to the base, the assembly including a rodengaging the keytop, and means for moving the rod along a path ofdistance d relative to the base responsive to keytop stroking, and forrestoring the rod to its former position as the stroking force isremoved, the base and assembly constituting a unitary flexible toughbody, wherein the translating means comprise:

a cantilever beam secured to the base at one end thereof and includingmeans for forming a spaced and rigid hinging engagement of length 1between the other end of the and the rod, the beam flexing as the rodmoves; and means for limiting the excursion of the rod with respect tothe beam and the base such that an angle 0 between the beam longitudinalaxis and the rigid hinging engagement axis lies within the range 0 5 coswhereby the resulting composition of forces urged by the beam upon therod includes a force component lying in the restoring force direction.

12. In a mechanical key actuator according to claim 11, where therestoring force component F varies as a simple sinusoidal function ofangle 0 for 0 s 0 qr/n, n 2 and as a complex sinusoidal function for1r/n s 0 1r/2.

1. In an actuating device more particularly adapted to electric switchesand having a keytop, a base, and an actuator assembly affixed to thebase, the assembly including an actuating rod mechanically engaging thekeytop, and means for translating the rod along a defined path relativeto the base responsive to keytop stroking, and for restoring the rod toits former position in the absence of stroking, the base and theassembly constituting a unitary flexible tough thermoplastic body;wherein the translating means comprise: hinging means; a first andsecond rigid member; a first and second beam member secured to the baseat one of their ends and forming at the other of their ends a hingingengagement with the rod through the hinging means and the correspondingrigid member, each beam member being deflected by a corresponding rigidmember as the rod translates; and means for limiting the excursion ofthe rod such that an acute angle is maintained between the longitudinalaxis of each beam member and the axis of the hinging means andcorresponding rigid member.
 2. In an actuating device according to claim1, wherein: the flexible-tough thermoplastic body is formed from amaterial selected from at least one of the group consisting ofpolypropylene, nylon, delrin, polyethylene, polyphenylene oxide, andinjection moldable polyurethane.
 3. In an actuating device according toclaim 1, wherein: the keytop forms a substantially hollowed out cavityfacing one surface of the base and being spaced apart therefrom suchthat a distinct acoustic wave is generated upon the keytop being strokedand the cavity impacting the base surface.
 4. In an actuating devicemore particularly adapted to electric switches and having a keytop, abase, and an actuator assembly affixed to the base; the assemblyincluding an actuating rod mechanically engaging the keytop; and meansfor translating the rod along a defined path relative to the baseresponsive to keytop stroking, and for restoring the rod position in theabsence of stroking, the base and assembly constituting a unitaryflexible tough body; wherein: the translating means comprise: acantilever beam arrangement secured to the base at one end thereof andfurther including means for forming a spaced and rigid hingingengagement between the other end of the beam arrangement and the rod,the beam arrangement flexing as the rod translates: and means forlimiting the excursion of the rod such that an acute angle is maintainedbetween the flexing beam arrangement and the axis of its spaced andrigid hinging engagement to the rod.
 5. In an actuating device accordingto claim 4, wherein: the cantilever beam arrangement comprises: asubstantially cylindrically shaped flexing member surrounding at least aportion of the rod extent, the cylindrical flexing member being securedto the base at one of its ends; and rigid diaphragm means hingedlyattached to the other cylindrical flexing member end along the diaphragmouter periphery and hingedly attached to the rod along the diaphragminner periphery.
 6. In an actuating device according to claim 4,wherein: the base and assembly constituting the unitary body are formedfrom a flexible-tough thermoplastic material.
 7. In an actuating deviceaccording to claim 4, wherein: the base and assembly constituting theunitary body are formed from a material selected from at least one of agroup of materials consisting of polypropylene, nylon, delrin,polyethylene, polyphenylene oxide, and moldable polyurethanes.
 8. In anactuating device according to claim 4, wherein: the base and assemblyconstituting the unitary body are formed from polypropylene suffusedwith antimony oxide.
 9. In an actuating device according to claim 8,wherein: the antimony oxide constitutes no more than 20 percent of thepropylene and antimony oxide volume.
 10. In an actuating deviceaccording to claim 4, wherein: each hinging engagement is fashioned froma segment of thermoplastic material having a cross section thickness Tparallel to the hinging axis in the range 0.001 inches < or = T < or =0.01 inches and further wherein the long chain polymers are orientedtransverse to the hinging axis.
 11. In a mechanical key actuator havinga keytop, a base, and an actuator assembly affixed to the base, theassembly including a rod engaging the keytop, and means for moving therod along a path of distance d relative to the base responsive to keytopstroking, and for restoring the rod to its former position as thestroking force is removed, the base and assembly constituting a unitaryflexible tough body, wherein the translating means comprise: acantilever beam secured to the base at one end thereof and includingmeans for forming a spaced and rigid hinging engagement of length lbetween the other end of the beam and the rod, the beam flexing as therod moves; and means for limiting the excursion of the rod with respectto the beam and the base such that an angle theta between the beamlongitudinal axis and the rigid hinging engagement axis lies within therange whereby the resulting composition of forces urged by the beam uponthe rod includes a force component lying in the restoring forcedirection.
 12. In a mechanical key actuator according to claim 11, wherethe restoring force component F varies as a simple sinusoidal functionof angle theta for theta < or = theta < pi /n, n > 2 and as a complexsinusoidal function for pi /n < or = theta < pi /2.